This invention relates to an arrangement for the suppression of signal interference, which arrangement comprises two transmission networks which electrically connect an electric signal source to a processing circuit for computing the interference-free useful signal.
Measuring quantities which are detected and converted into a transmissible electrical quantity by electronic sensors are susceptible to the influence of interference during the transmission from the measurement location to the processing and display circuit. In order to process the information contained in the useful signals the useful signals must be freed of interference.
Correlation methods for the elimination of spurious components are described in the book by G. Ehrenstrasser, "Stochastische Signale und ihre Anwendung" from Dr. A. Huthig Verlag, Heidelberg, pages 82 to 84. These methods are employed for the detection of signals with a very high noise level. The useful signals which appear simultaneously across two measurement sensors are transferred via two measuring channels which are influenced by interference independently of each other. At the end of the transmission path these measuring channels are connected to a cross-correlator which generates the cross-correlation function for the delay time .tau.=0 from the two disturbed signals transmitted by the two channels. The correlator computes the square of the effective values of the useful signals because only the identical useful signals are correlated to each other. Since neither the interference signals and useful signals nor the interference signals of both channels are statistically related to each other all further products of the effective values of the useful signal and the interference signals and of the two interference signals computed by the correlator are zero. However, if the interference signals which influence the two measuring channels are not statistically independent of each other, as for example in the case of electromagnetic interference influencing the transmission lines, the correlator will compute a non-zero product for the effective values of the interference signals superimposed on the square of the effective values of the useful signals at the output of the correlator. Thus, the known correlation method is not capable of removing those spurious signals from the useful signal which act over a larger area and thus may influence several component parts at the same time.